In recent years, electronic cameras are popularly used. In this kind of the electronic camera, image data captured by means of a CCD image sensor and so forth is converted into digital data and is stored in a memory. Meanwhile, storage capacity of the memory increases in accordance with high integration thereof and moving-image compression technique is improved so that it becomes possible to take a moving image. Consequently, some of the commercial electronic cameras are capable of performing both of still-image shooting and moving-image shooting.
When shooting is performed with the electronic camera, it is possible to utilize an LCD panel as an electronic viewfinder besides a built-in optical viewfinder. On the LCD panel, a subject image formed on the CCD image sensor is continuously displayed. Many electronic cameras are provided with an autofocus function of an active system using infrared rays, for the purpose of performing focus adjustment at a time of shooting. Among the electronic cameras, there is a single-lens reflex type provided with a manual focus function capable of manually adjusting the focus.
When the manual focus function is used in taking an image, a shooter visually finds a focal point by utilizing the LCD panel and the optical viewfinder. However, since a pixel number of the LCD panel is extremely small in comparison with that of the image sensor, the image displayed thereon is grainy and it is difficult to finely perform the focus adjustment. Moreover, when the LCD panel is used, quality of the viewfinder image displayed thereon further deteriorates due to dropping frames of the subject image continuously displayed.
In this regard, Japanese Patent Laid-Open Publication No. 2002-209135 proposes a method in which focus aid is performed by using a width of an edge detected from an image at a time when the focus is manually adjusted in the electronic camera. A user judges a degree of focus on the basis of a bar graph showing an evacuation result of the edge displayed on the LCD panel.
Japanese Patent Laid-Open Publication No. 2004-040740 proposes a method in which a stop is vertically moved relative to an optical axis and a focus condition is displayed on the basis of image fluctuation to perform the focus adjustment. An aperture stop is provided so as to be movable at an optical path of a subject from side to side. A split image is produced from images obtained when the aperture stop is shifted to the right side and to the left side. The produced split image is displayed on a monitor.
Japanese Patent Laid-Open Publication No. 2005-025055 proposes a method in which a user manually and correctly performs focus adjustment of a taking lens even when the attached taking lens is not supported by the autofocus function. A focal position of a manual focus lens is detected by using an AF sensor. At the identical lens position, the focal position is detected in another way on the basis of contrast change of a subject image formed on an image sensor. Based on the result of the detected focal positions, a built-in main CPU calculates correction data for correcting a focus shift amount in displaying focus aid. On the basis of the calculated correction data, the focus aid is displayed.
In Japanese Patent Laid-Open Publication No. 2002-333569, low-pass filter processing of an image is abbreviated to facilitate focus adjustment performed by using a monitor image.
However, some of the above-mentioned methods are complicated and it is generally difficult to adjust the focus because a change of the focus is confusing in the manual focus using an electronic camera comprising a monitor of an LCD viewfinder type or the like. Further, there is an unsolved fatal problem in that it is turned out after shooting that the focus was not adjusted even though the focus seemed to be adjusted on the monitor.